[PATCH V2] dt-bindings: nvmem: u-boot,env: add Broadcom's variant binding

[Rafał Miłecki]

On 18.10.2022 12:19, Conor Dooley wrote:
> On Fri, Oct 14, 2022 at 04:09:40PM -0500, Rob Herring wrote:
>> On Fri, 30 Sep 2022 18:36:31 +0200, Rafał Miłecki wrote:
>>> From: Rafał Miłecki <rafal at milecki.pl>
>>>
>>> Broadcom uses U-Boot for a lot of their bcmbca familiy chipsets. U-Boot
>>> stores its configuration in an environment data block.
>>>
>>> Such blocks are usually stored on flash as a separated partition at
>>> hardcoded address. Broadcom however decided to:
>>> 1. Store env data block inside U-Boot partition
>>> 2. Avoid sticking to hardcoded offsets
>>> 3. Use custom header with "uEnv" magic and env data length
>>>
>>> Example (length 0x4000):
>>> $ hexdump -n 32 -C -s 0x40000 /dev/mtdblock0
>>> 00040000  76 6e 45 75 00 40 00 00  34 89 7a 82 49 4d 41 47  |vnEu. at ..4.z.IMAG|
>>> 00040010  45 3d 4e 41 4e 44 3a 31  4d 2c 31 30 32 34 4d 00  |E=NAND:1M,1024M.|
>>> (0x40000 offset is unit specific and can change)
>>>
>>> Starting with the commit 118f3fbe517f4 ("dt-bindings: mtd: partitions:
>>> support label/name only partition") DT can describe partitions matching
>>> them by a name (without specifying actual address). With that feature
>>> and this binding change it's possible to:
>>> 1. Specify DT node for Broadcom's U-Boot env data subpartition
>>> 2. Add nodes for specific environment data variables
>>> 3. Reference them as NVMEM cells
>>>
>>> This binding is unlikely to help Broadcom's U-Boot. U-Boot SPL needs to
>>> find environment data early (before it accesses DTB) and it does that by
>>> looking for an "uEnv" magic. Dirty way.
>>>
>>> This binding can however be used by operating systems. It allows
>>> describing cleanly U-Boot, its env data and variables. It tells
>>> operating system about Broadcom-specific env data so it can parse it.
>>>
>>> Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
>>> ---
>>> V2: Work on better commit body & add example
>>> ---
>>>   .../devicetree/bindings/nvmem/u-boot,env.yaml | 21 +++++++++++++++++++
>>>   1 file changed, 21 insertions(+)
>>>
>>
>> Applied, thanks!
> 
> Hey Rob,
> Maybe my tooling is out of date or w/e but this is breaking
> dt_binding_check for me.
> 
> I applied the below to fix the build, which I was about to send, before
> realising that you'd applied it and wondered if I was missing something.

Thanks for catching that and submitting a fix!

I guess I didn't run dt_binding_check this time or I did it before
adding an example. Sorry for that!